1. Characterizing the Skeletal Phenotype of db/db Mice Student: Bailey Lindenmaier Mentors: Dr. Russell Turner & Dr. Urszula Iwaniec Skeletal Biology Lab

2. Introduction Age related Osteoporosis- Porous bone 1 in 3 women and 1 in 5 men over the age of 50 worldwide are estimated to have osteoporosis In 2005, osteoporosis-related fractures were responsible for an estimated $19 billion in costs. Health risks ▫ Increases individuals risk of fractures ▫ Following peak bone mass, lost bone mass is difficult to restore

3. Leptin Product of the OB gene Primarily produced by adipose tissue. Pleiotropic hormone ▫ Appetite control ▫ Energy regulation ▫ Immune response ▫ Cardiovascular and renal function Essential for achieving optimal peak bone mass.

4. Identifying the Mechanism of Leptin on Bone Remodeling Leptin is a key hormone in regulating and maintaining healthy bones. Early work suggests that s.c. leptin injection reduced bone loss following ovx. Current data proposes that leptin functions via the CNS. Osteoblast express leptin receptor. Possible peripheral affect? Answers may lead to a generation of drugs to treat osteoporosis.

5. Proposed Pathways of Leptin’s Effects on the Skeleton Leptin ObRb Receptor

6. db/db mice Loss of function in the leptin receptor Mosaic skeletal type ▫ Overall reduced bone mass ▫ High cancellous bone mass of vertebrae. ▫ Low bone mass in femur. ▫ Decreased length of femoral bones. Obese, hypogonadic, hyperinsulemic, hypercortisolic db/dbWild Type

7. Goal Characterize skeletal growth of WT and leptin-deficient db/db mice.

8. Study Design A group of 10 WT and db/db mice sacrificed at 8 weeks for baseline. A group of 7 WT and db/db mice sacrificed at 17 weeks. Fed ad libitum, 12h light/dark cycle Both femurs and LV 5 were excised at necropsy B6.BKS(D)-Lepr db

9. µ CT Analysis Micro - Computed Tomography Fires an x-ray beam at a rotating specimen Produces 3D images for structural measurements

10. Femoral cortex Femur Metaphysis (trabecular bone) Bones Analyzed Vertebral Cancellous Bone

11. Femur Length 8 weeks17 weeks Total Femur Bone Volume 8 weeks17 weeks db/db Results 00 ANOVA Effects Genotype: p<.001 Age: p<.002 Genotype x Age: p<.004 ANOVA Effects Genotype: p<.001 Age: p<.001 Genotype x Age: p<.002

12. Femur Cortical Thickness 8 weeks17 weeks db/db Results 0 Diaphysis- Cortical Bone ANOVA Effects Genotype: p<.001 Age: p<.001 Genotype x Age: p<.001

13. Metaphysis Bone Volume/Tissue Volume 8 weeks17 weeks db/db Results ANOVA Effects Genotype: N.S Age: p<.001 Genotype x Age: p<.038

14. Lumbar Vertebrae 5 Bone Volume/Tissue Volume 8 weeks17 weeks db/db Results 0 ANOVA Effects Genotype: p<.001 Age: p<.026 Genotype x Age: p<.007

15. Lumbar Vertebrae 5 Trabecular Thickness 8 weeks17 weeks 8 weeks17 weeks Lumbar Vertebrae 5 Trabecular Number Results 0 ANOVA Effects Genotype: p<.001 Age: p<.001 Genotype x Age: p<.004 ANOVA Effects Genotype: N.S Age: p<.001 Genotype x Age: N.S

16. Conclusions Aging db/db mice have high bone mass in their lumbar vertebrae ▫ Maintain trabecular number ▫ Increase in trabecular thickness Aging db/db mice have low bone mass in their femur. ▫ Low cortical thickness ▫ Reduced femoral length

17. On the Horizon Histomorphometric analysis of bone. Bone marrow transplantation following irradiation to determine if leptin has a direct effect on bone remodeling.

18. Acknowledgements Dr. Russell Turner Urszula Iwaniec Dawn Olson Kenneth Philbrick Kevin Ahern Howard Hughes Medical Institute